In the field of video compression, communication, decompression, and display, there has been for many years problems associated with supporting both interlaced content and interlaced displays along with progressive content and progressive displays. Many advanced video systems support either one or the other format. As a result such devices as deinterlacers became an important component in many video systems. Deinterlacers convert interlaced video content into progressive video format.
Deinterlacing takes interlaced video fields and coverts them into progressive frames, at double the display rate. Certain problems may arise concerning the motion of objects from image to image. Objects that are in motion are encoded differently in interlaced fields from progressive frames. Video images, encoded in deinterlaced format, containing little motion from one image to another may be deinterlaced into progressive format with virtually no problems or visual artifacts. However, problems arise with video images containing a lot of motion and change from one image to another, when converted from interlaced to progressive format. As a result, some video systems were designed with motion adaptive deinterlacers.
Today, motion adaptive deinterlace video systems rely on multiple fields of data to extract the highest picture quality from a video signal. Combining multiple fields of data for deinterlacing can only be done when all the fields are the same size image. Hence, the system expects the input image to be a certain size, and all the processing that the system carries is designed to accommodate the specific expected image size.
Typically, broadcasted analog standard definition (SD) images are sampled at 720×480 frames in progressive systems or 720×240 fields in interlaced systems. Hence, analog signals coming in are always 720 wide. When the channel is changed from one SD channel to another SD channel, the broadcast still has the same format, with a width of 720 pixels per line.
However, in many video systems such as, for example, broadcast MPEG systems, sending images with width less than 720 pixels provides savings in the satellite and in the cable system. A certain channel may get broadcasted at 352×480 format and another channel may get broadcasted at 720×480 format. A viewer does not notice the change when watching it, since as the channels change, the digital receiver takes the channel inputs and scales them to a fixed size that fits the viewer's screen.
The change in the field size creates a problem, which is that existing deinterlacer circuits fail at the boundaries between video frames with different sizes. During a deinterlacing process, in order to compare one line in a field to the same line in a field two fields ago, the two fields have to have the same width. If, during the middle of a transmission, the horizontal size of a field changed on the fly, in the case of 352×480 and 720×480 formats, the deinterlacer is suddenly trying to compare 352 samples to 720, which will not work.
Existing systems either, ignore this problem and incorrectly deinterlace objects of different sizes, or the deinterlacer is turned off during a dynamic format change. A common approach to this problem is when there is a change in the input image size, the deinterlacer is disabled and the video is passed through the system, until the system is flushed and the new data and the new width are recovered. Hence, when the resolution at the broadcaster end is changed, the viewer is looking at a screen and all of a sudden the screen gets fuzzy, then a half second later the screen gets sharp again, which may be irritating to a viewer.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.